An apparatus and method for determining connected substructures within a body is disclosed. The system and method are particularly advantageous for use in medical diagnostic imaging applications. In particular, three dimensional regions exhibiting the same tissue type are similarly labeled. Using the label information together with a seed location located in the substructure of interest, all similarly labeled connected data points are determined. The system and method of the present invention is operable in any situation in which three dimensional signal patterns representing the value of one or more physical properties associated with the substructures within a body at regularly grid locations within the body are presented. A subset of the original data is then provided to a display processor particularly one employing gradient normal shading for display of three dimensional images.